U.S. patent number 3,757,053 [Application Number 05/179,344] was granted by the patent office on 1973-09-04 for time multiplexed sampled data telephone system.
This patent grant is currently assigned to Delta Communications Corp.. Invention is credited to Steven T. Churchill, Richard B. Pell, William Seeley.
United States Patent |
3,757,053 |
Pell , et al. |
September 4, 1973 |
TIME MULTIPLEXED SAMPLED DATA TELEPHONE SYSTEM
Abstract
In a telephone system, audio signals to and from each telephone
in the system are connected to a time division, amplitude
modulated, multiplexed sampled data transmitting and receiving
means by a pair of wires. Each telephone in the system may be used
to receive paging or music signals, to make a call when it has been
called, to intercept a conversation between two other telephones,
to forward a call intended for it to another telephone, to complete
a call directed to one of a group of telephones with any one
telephone in the group which is not busy, and to provide a hands
free operation at a called telephone. The various uses are selected
by connecting a D.C. voltage, via each pair of wires, to each of
the telephones, having the telephones draw currents according to
desired modes of operation, and having the time multiplexed
transmitter process audio signals according to the currents
drawn.
Inventors: |
Pell; Richard B. (Wantagh,
NY), Churchill; Steven T. (North Bennington, VT), Seeley;
William (Williamstown, MA) |
Assignee: |
Delta Communications Corp.
(Plainview, NY)
|
Family
ID: |
22656182 |
Appl.
No.: |
05/179,344 |
Filed: |
September 10, 1971 |
Current U.S.
Class: |
370/271; 379/157;
379/251; 381/77 |
Current CPC
Class: |
H04Q
11/04 (20130101) |
Current International
Class: |
H04Q
11/04 (20060101); H04q 011/00 (); H04m
003/42 () |
Field of
Search: |
;179/15AL,15BM,15BY,1H,37-40,18AD,2.5R,84SS,18B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; Thomas W.
Claims
What is claimed is:
1. A telephone communications system comprising:
a plurality of telephones each of which originates and receives
calls, and each of which includes a variable resistive load;
a time division, amplitude modulated, multiplexed transmitting and
receiving means for transmitting and receiving calls;
electrical conductor means coupling each of said plurality of
telephones to said time multiplexed transmitting and receiving
means;
means forming part of said transmitting and receiving means for
supplying a D.C. voltage to each of said plurality of telephones
via its respective conductor means; and
means responsive to the current drawn by each of said plurality of
telephones for routing calls for a first of said plurality of
telephones to a second of said plurality of telephones.
2. A telephone communications system as defined in claim 1 wherein
said time multiplexed transmitting and receiving means includes
means for terminating an unanswered call from said first of said
plurality of telephones to any other of said plurality of
telephones after a predetermined time interval.
3. A telephone communications system as defined in claim 1, further
including means for providing paging or music signals to said first
of said plurality of telephones via its corresponding conductor
means.
4. A telephone communications systems as defined in claim 1,
further including a light source coupled to said conductor means,
and wherein said time multiplexed transmitting and receiving means
includes means coupled to said conductor means for lighting said
light source.
5. A telephone communications system as defined in claim 1, further
including an audio transceiver coupled to said conductor means, and
wherein said time multiplexed transmitting and receiving means
includes means responsive to the current drawn by a second of said
plurality of telephones for controlling audio signal traffic at
said audio transceiver.
6. A telephone communications system as defined in claim 1, wherein
said plurality of telephones includes a group of telephones, and
said time multiplexed transmitting and receiving means includes
means for directing a call from said first of said plurality of
telephones to any one of said group of telephones which is not
receiving a call.
7. A telephone communications system as defined in claim 1, wherein
said routing means includes means for routing a call from a first
of said plurality of telephones, directed to a second of said
plurality of telephones, to a third of said plurality of
telephones.
8. A telephone communications system as defined in claim 7 wherein
said time multiplexed transmitting and receiving means includes
means for terminating an unanswered call from said first of said
plurality of telephones to any other of said plurality of
telephones after a predetermined time interval.
9. A telephone communications system as defined in claim 7, further
including means for providing paging or music signals to said first
of said plurality of telephones via its corresponding conductor
means.
10. A telephone communications system as defined in claim 7,
further including a light source coupled to said conductor means,
and wherein said time multiplexed transmitting and receiving means
includes means coupled to said conductor means for lighting said
light source.
11. A telephone communications system as defined in claim 7,
further including an audio transceiver coupled to said conductor
means, and wherein said time multiplexed transmitting and receiving
means includes means responsive to the current drawn by a second of
said plurality of telephones for controlling audio signal traffic
at said audio transceiver.
12. A telephone communications system as defined in claim 7,
wherein said plurality of telephones includes a group of
telephones, and wherein said time multiplexed transmitting and
receiving means includes means for directing a call from said first
of said plurality of telephones to any one of said group of
telephones which is not receiving a call.
13. A telephone communications system as defined in claim 12,
further including means for providing paging or music signals to
said first of said plurality of telephones via its corresponding
pair of wires.
14. A telephone communications system as defined in claim 12,
wherein said time multiplexed transmitting and receiving means
includes means for terminating an unanswered call from said first
of said plurality of telephones to any other of said plurality of
telephones, after a predetermined time interval.
15. A transceiver for a time-multiplexed sampled data telephone
system, comprising:
a first audio line;
a second audio line;
a telephone for transmitting and receiving electrical signals;
a pair of wires coupled to said telephone;
means for providing a first periodic pulse signal, in a variable
time slot, coupled to said pair of wires;
means for providing a second periodic pulse signal in a
predetermined time slot;
first pulse responsive means coupling said first audio line to said
pair of wires;
first and second demodulators coupled to said pair of wires;
second pulse responsive means coupling said second audio line to
said first demodulator;
third pulse responsive means coupling said second audio line to
said pair of wires;
fourth pulse responsive means coupling said first audio line to
said second demodulator; and
means for selectively coupling said first periodic pulse signal to
said third and fourth pulse responsive means or coupling said first
periodic pulse signal to said first and second pulse responsive
means and said second periodic pulse signal to said third and
fourth pulse responsive means.
16. A transceiver as defined in claim 15, including:
a busy signal generator; and
means coupling said busy signal generator to said pair of
wires.
17. A transceiver as defined in claim 16, wherein said means
coupling said busy signal generator to said pair of wires
includes:
a busy switch;
a busy gate coupled to said busy switch;
a power switch coupled to said busy gate and to said privacy
switch; and
a privacy line coupled to said privacy gate.
18. A transceiver as defined in claim 15, including:
a ring tone generator; and
means coupling said ring tone generator to said pair of wires.
19. A transceiver as defined in claim 18, wherein said means
coupling said ring tone generator to said pair of wires
includes:
a ring control line;
a ring receiver coupled to said ring control line and to said means
for providing a second periodic pulse signal;
a ring switch coupled to said ring tone generator and to said ring
receiver; and
a transformer coupling said ring switch to said pair of wires.
20. A transceiver as defined in claim 15 including:
a bleep tone generator; and
means coupling bleep tone generator to said pair of wires.
21. A transceiver as defined in claim 20, wherein said means
coupling said bleep tone generator to said pair of wires
includes:
a power switch;
a call intercept latch coupled to said power switch;
a bleep network coupled to said call intercept latch and said bleep
tone generator;
a ring switch coupled to said bleep network and said power switch;
and
a transformer network coupling said ring switch to said pair of
wires.
22. A transceiver as defined in claim 15 including:
a paging and music signal generator; and
means coupling said paging and music signal generator to said pair
of wires.
23. A transceiver as defined in claim 22, wherein said means
coupling said page-music generator to said pair of wires
includes:
a ring coupled to said page-music generator;
a power switch coupled to said ring switch; and
a transformer network coupling said ring switch to said pair of
wires.
24. A transceiver as defined in claim 23, including:
a busy signal generator;
means coupling said busy signal generator to said pair of
wires;
a ring tone generator;
means coupling said ring tone generator to said pair of wires;
a bleep tone generator;
ameans coupling said bleep tone generator to said pair of
wires;
a light pulse generator;
a light bulb coupled to said pair of wires; and
means coupling said light pulse generator to said pair of wires.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates to communications systems and in
particular to a telephone communications system wherein the system
telephones are connected to a time multiplex transmitter by a
single pair of wires.
2. Description of the Prior Art
Existing telephone systems have conference call capabilities, call
transfer capabilities, call intercept capabilities, "hands free"
operation capabilities, call forward capacilities, ring-out
capabilities, group hunt capabilities and indicator lights.
However, telephone systems having all of the capabilities mentioned
above which accommodate 20 or fewer telephones require that many
wires be connected to each telephone from a central station. In
telephone systems having a greater telephone capacity, it has been
necessary to install expensive banks of automatic or semiautomatic
switching devices of either the so-called step-by-step or cross bar
types. Moreover, in these systems, some of the functions above
described are only available with the aid of a switchboard and an
operator.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an
improved time-multiplexed sampled data telephone system.
It is another object of this invention to provide a telephone
system wherein a called telephone can add another telephone to the
conversation without the assistance of an operator.
It is a further object of this invention to provide a telephone
system wherein calls to any one telephone may, automatically, be
transferred to another telephone without the assistance of an
operator.
It is another object of this invention to provide a telephone
system wherein calls to a particular telephone may be intercepted
by another telephone without the assistance of an operator.
It is an additional object of this invention to provide a telephone
system wherein all telephones may be used simultaneously.
It is another object of this invention to provide a telephone
system wherein each telephone provides music or a public
address.
It is a further object of this invention to provide a telephone
system wherein a called telephone may be answered without the need
to lift or hold the handset of the called telephone.
It is still another object of this invention to provide a telephone
system wherein a calling telephone is automatically disconnected
within a predetermined time after a called party hangs up his
telephone, or within a predetermined time if a called telephone is
unanswered.
It is yet another object of this invention to provide a telephone
system wherein a call to any one of a group of associated
telephones will be completed with an available telephone in the
group.
It is a further object of this invention to provide a telephone
system wherein telephones in the system include a bulb which lights
up when its associated telephone rings.
It is also an object of this invention to provide a telephone
system wherein each telephone in the system is connected to the
rest of the system by a single pair of wires.
The system of the present invention has all these capabilities
although each telephone is connected to a central station by only
two wires, because the central station includes a time division,
amplitude modulated, multiplexed transmitting and receiving means,
which is described below.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned and other objects of this invention will become
apparent by reference to the following description which is to be
read, in conjunction with the accompanying drawings, wherein:
FIG. 1 is a block diagram of a telephone system according to the
invention;
FIG. 2 illustrates voltage waveforms associated with the telephone
system according to the invention;
FIG. 3 is a schematic diagram of a subsystem according to the
invention;
FIG. 4 is a block diagram of subsystems used according to the
invention when Telephone A calls Telephone B;
FIG. 5 is a block diagram of subsystems used according to the
invention when Telephone A intercepts an existing conversation;
FIG. 6 is a block diagram of subsystems used according to the
invention when Telephone A forwards calls to it to another
telephone;
FIG. 7 is a block diagram of subsystems used to provide a public
address or music to telephones otherwise not in use;
FIG. 8 is a block diagram of subsystems used to provide a "hands
free" operation of a telephone;
FIG. 9 is a block diagram of subsystems used to provide a "group
hunt" function according to the invention;
FIG. 10 is a block diagram of subsystems used according to the
invention which cause a light to blink at a ringing telephone;
FIG. 11 is a block diagram of subsystems used according to the
invention which cause a calling telephone to be disconnected from a
called telephone;
FIG. 12 is a schematic diagram of a link exchange network according
to the invention;
FIG. 13 is a schematic diagram of a privacy switch according to the
invention;
FIG. 14 is a schematic diagram of a privacy gate according to the
invention; and
FIG. 15 is a schamatic diagram of a ring disable receiver according
to the invention.
The complex system to be described as an embodiment of the
invention utilizes many sybsystems, only some of which deserve
attention herein. Accordingly, the subsystems will first be
described functionally with respect to the various operational
modes of the system and then, where not obvious to one having
ordinary skill in the art, with respect to how they achieve their
function.
Referring to FIG. 1, in a 100 telephone system, 100 telephones
A,B,C, . . . F, (all not shown) are each connected, respectively,
to 100 corresponding logic cards L.sub.A, L.sub.B, L.sub.C . . .
L.sub.F, located at a central station 10, in the form of a time
multiplexed transmitter, by 100 pairs of telephone wires, W.sub.A,
W.sub.B, W.sub.C . . . W.sub.F. At the central station 10, there is
connected to each logic card a bleep tone generator 14 via line 30,
a page-music generator 11 via line 28, a ring tone generator 12 via
line 27, light-pulse generator 15 via line 26, a busy signal
generator 13 via line 29, a common talk line 16, a common talk line
17, a ring control line 18, a privacy line 19, a privacy line 20, a
ring disable line 21, a stepping line 22, a hold line 23, a
push-to-talk line 24 and the 16 output lines 32 thru 47 of an 8-bit
counter 48 which includes a clock. The output signals of lines 40
through 47 respectively, are the logic complements of the output
signals on lines 32 through 39.
The 8-bit counter 48 provides periodically, in binary form, numbers
N which range from 1 to 100 at a rate equal to the frequency of the
8-bit counter clock divided by 100. Each binary number
corresponding to a number N appears during a particular time
interval of the periodic 8-bit counter cycle and is used to
identify a periodic time interval. The defined periodic time
intervals are used in the system to identify each system telephone,
for connecting one telephone to another, and to provide timing
signals for a time multiplexed sampled-data arrangement which is
used to transmit audio signals from one telephone to another.
Referring to FIGS. 1, 2, 3, and 4, each of the 100 telephones in
the system is assigned one of the numbers N, from 1 to 100, which
corresponds to a binary count in the 8-bit counter 48 and each
logic card includes a fixed time slot decoder (such as 101 and 201
in logic cards L.sub.A and L.sub.B) which is programmed in
accordance with its assigned binary number, to produce pulses
periodically in its related time slot. The pulses on each logic
card comprise a periodic signal, herein referred to as T.sub.N, as
shown in FIG. 2a.
Referring to FIG. 3, the periodic signal, is achieved for example,
on logic card L.sub.A, which is assigned number 46, by connecting
the 16 outputs 32 through 47 of the 8-bit counter 48, respectively,
to input terminals 49 through 64 on fixed time slot decoder 101 and
connecting the 8 inputs of the AND gate 65 to those terminals which
are at a logic 1 level when binary number 46 is present in binary
form (01000110) at the 8-bit counter 48. As is well known, this
arrangement provides an output pulse only when the binary number 46
is present and, where as here, when the binary number is
periodically applied, a periodic pulse signal T.sub.46 is
provided.
How the T.sub.N signals are processed by the respective logic cards
in the system will be described herein below in connection with
FIG. 4, which shows in block diagram form the subsystems located on
logic cards L.sub.A, L.sub.B, used when a direct call is made from
telephone A to telephone B. Telephone A and Telephone B have,
respectively, assigned numbers 46 and 26.
Referring to FIG. 4, Telephone A includes an audio transformer (not
shown) whose secondary winding is connected by wires W.sub.A to the
primary winding (not shown) of a transformer in transformer network
103. A D.C. voltage from power switch 107 is connected by wire 106
to commutator 105 (hereinafter described) and by wire 104 to the
primary winding of the transformer in the transformer network 103
to supply DC current to Telephone A. Telephone A includes a dialing
arrangement and special system function switches (not shown) for
"call forward" and "call intercept" modes of operation, hereinafter
described, when when operated cause the D.C. current being
delivered to Telephone A to change by detectable amounts. For
example, when the Telephone A handset is in its cradle zero ma
flow; when the handset is lifted from the cradle a hook switch (not
shown) is closed and 46 ma flow; when the "call intercept" switch
is closed, 62 ma flow; and when the call forward switch is closed,
more than 100 ma flow. The power switch 107 senses the current
being drawn and provides output voltages which the logic card
L.sub.A requires in order to operate in the desired mode.
When the handset of Telephone A is picked up to make a call at time
t=0, the hook switch closes and power switch 107 senses that 46 ma
are being drawn. In response, the power switch provides voltages,
as shown in FIGS. 2b, c, d, and e, PS, PS, PPS, and PPS,
respectively, over lines 108, 109, 110, and 111 to subsystems on
logic card L.sub.A.
Line 108 is connected to ring switch 114, an electrically
controlled on-off switch, and to privacy switch 115, a circuit
which permits or blocks the passage of signal T.sub.46, generated
by the fixed time slot decoder 101, on to the privacy line 19.
Voltage PS closes the ring switch 114 and causes the privacy switch
115 to block signal T.sub.46 when the handset of Telephone A is
lifted. Further, when the handset is lifted, the ring switch 114 is
closed, and it connects the transformer network 103, via line 116,
to the dial register 117, a circuit which stores dialed pulses in
binary form, and to the audio line 118.
Line 109 is connected to busy gate 119, a circuit which activates
an electrical busy switch 120. Busy switch 120 couples a busy tone
on line 29 to audio line 118 when the called telephone is busy.
Voltage PS disables the busy gate 119 when Telephone A is not in
use.
Line 110 is connected to ring gate 121, a circuit which permits or
blocks the passage of a signal to ring control line 18 for causing
Telephone B to ring, and to the dial register 117. The voltage PPS
on line 110 enables the ring gate 121 and clears the dial register
117 when the handset of Telephone A is lifted.
Line 111 is connected to privacy gate 122, a circuit which
generally compares periodic pulse signals from privacy line 19 with
a periodic signal on line 124 from variable time slot decoder 123.
The privacy gate 122 provides, when there is coincidence, between
the signals on line 19 and 124 a periodic signal V'.sub.26 on line
125 which is connected to ring gate 121 and link exchange network
126; and a signal which is connected via line 127 to busy gate 119
for diabling the busy switch 120. The voltage PPS disables the
privacy gate 122 when the handset of Telephone A is lifted. Line
111 is also connected to dial register 117 and clears it when the
handset of Telephone A is returned to its cradle.
When the number (26) of Telephone B is dialed on Telephone A, it
provides, sequentially, a pair of pulses which represent the number
2 and a set of 6 pulses which represent the number 6. The pulses
from Telephone A are transmitted via wires W.sub.A to the
transformer network 103 and to the dial register 117 via ring
switch 114 which was closed by voltage PS. The dial register counts
the pulses, stores them as binary number 26 (00100110) and provides
this binary number over lines 126 through 133 to variable time slot
decoder 123 which also receives, over lines 32 through 39, from the
8-bit counter 48, binary numbers ranging from 1 to 100. The
variable time slot decoder 123 compares its two sets of binary
inputs and provides a pulse whenever there is coincidence. Since
the output of the 8-bit counter 48 is periodic, the resulting
signal from the variable time-slot decoder 123 is a periodic pulse
signal V.sub.26 which is substantially similar to periodic pulse
signal T.sub.26 provided by the fixed time slot decoder 201 on
logic card L.sub.B.
The V.sub.26 signal from the variable time-slot decoder 123 is
connected by wire 124 to the privacy gate 122 and to the busy gate
119 which in turn closes the busy switch 120 thereby coupling a
busy tone from the busy signal generator 13 to audio line 118. The
busy tone on the audio line 118 travels through the ring switch 114
and transformer network 103 to Telephone A where a busy tone is
heard.
If Telephone B is not busy, the T.sub.26 signal which logic card
L.sub.B generates, is present on the privacy line 19 and at the
privacy gate 122. Privacy gate 122 is enabled when V.sub.26
.congruent. T.sub.26 and provides, over line 127, a signal which
overrides the V.sub.26 enabling signal over line 124 to the busy
gate 119, thereby leaving busy switch 120 open. Privacy gate 122
also provides a periodic pulse signal V'.sub.26 which is
substantially similar to V.sub.26 and is connected by line 125 to
ring gate 121. Ring gate 121 which was enabled by voltage PPS on
line 110 couples the V'.sub.26 signal to ring control line 18.
Ring control line 18 and the fixed time slot decoder 201 on logic
card L.sub.B are connected to ring receiver 234. The presence at
the ring receiver 234 of signals V'.sub.26 and T.sub.26 causes a DC
signal (0 logic level) to be transmitted over line 235 to ring
switch 214 and privacy switch 215. The DC signal at ring switch 214
causes the ring line 27 to be connected to the transformer network
203 and disables the privacy switch 215.
When ring switch 214 is closed by the DC level, ring tone on line
27 from the ring tone generator 12, as shown in FIG. 1, is coupled
via ring switch 214 to the transformer network 203 and from there
via wires W.sub.B, to Telephone B. The ring tone causes Telephone B
to ring, thereby announcing the presence of an incoming call. The
DC level connected to the privacy switch 215 via line 235 deprives
the privacy line 19 of signal T.sub.26 and thereby indicates to the
system that Telephone B is busy.
If the handset of Telephone B is picked up, as with Telephone A,
the power switch 207 provides PS and PS voltages over lines 208 and
209, respectively. Line 209 is connected to ring disable gate 236,
an electronic on-off switch which is turned on by voltage PS. When
the ring disable gate 236 is turned on, signal T.sub.26, which is
coupled thereto by line 202 from the fixed time slot decoder 201,
is connected to the ring disable line 21. The ring disable receiver
137 on logic card L.sub.A is connected to the ring disable line 21,
and to the variable time slot decoder 123 by line 124. The
simultaneous presence of both the V.sub.26 signal from the variable
time slot decoder 123 and the similar signal T.sub.26 from the ring
disable line 21 causes the ring disable receiver 137 to provide a
signal to line 138 which disables the ring gate 121. When the ring
gate 121 is disabled, signal V'.sub.26 does not reach the ring
control line 18, the DC level at the ring receiver 234 drops, the
ring tone is disconnected and Telephone B stops ringing. Line 208
connects voltage PS to privacy switch 215 when the handset of
Telephone B is picked up and maintains the privacy switch 215 in
the disabled state when the DC level drops, thereby continuing the
"in use" message to the system.
Line 208 also connects the power switch 207 to ring switch 214 and
voltage PS causes the ring switch 214 to connect line 216 to line
218 which carries audio signals.
When a person talking on Telephone A speaks, the audio signal
generated at the Telephone A is coupled via transformer network 103
and ring switch 114 to analog switch 141. Analog switch 141 only
allows the audio signal to pass through the analog switch 141 when
pulses from the privacy gate 122 are connected thereto by line 125,
link exchange network 126, and line 145. These pulses are provided
by signal V'.sub.26 ; therefore, the output of the analog switch
141 is a pulse amplitude modulated signal, whose pulses occur in
time slot 26. The modulated pulses are connected to the audio line
16. Line 16 is connected to analog switch 243 which is opened
periodically by signal T'.sub.26 connected thereto by line 202,
link exchange network 226, and line 246 from the fixed time slot
decoder 201. Since pulses from signals V'.sub.26 and T.sub.26 occur
at the same time, the analog switch 243 only passes the pulse
amplitude signal generated at logic card L.sub.A. The output of the
analog switch 243 is connected to a demodulator 244 which
reproduces the audio signal from Telephone A. The audio signal is
coupled to Telephone B by ring switch 214, and transformer network
203.
When a person talking on Telephone B replies, the reply audio
signal generated at Telephone B is coupled via transformer network
203 and ring switch 214 to analog switch 242; analog switch 242
only allows the reply audio signal to pass through the switch when
pulses from the signal T.sub.26 are coupled thereto on line 246.
Therefore, the output to line 17 of analog switch 242 is a pulse
amplitude modulated signal. The common talk line 17 is connected to
analog switch 140 which is periodically opened by the pulses from
signal V'.sub.26 and allows the pulse amplitude signal through. The
pulse amplitude signal at the output of the analog switch 140 is
connected to demodulator 139 which reproduces the audio reply
signal. The audio reply signal is connected to Telephone A via the
ring switch 114 and transformer network 103.
Referring to FIG. 5, logic card L.sub.A also includes an analog
switch 142 coupling the audio line 118 to common talk line 17, a
demodulator 144 coupled to the audio line 118, and an analog switch
143 coupling the common talk line 17 to the demodulator 144. Analog
switches 142 and 143 are connected to link exchange network 126 by
line 146. The link exchange network normally couples the periodic
signal T.sub.46 on line 102 from the fixed time slot decoder 101 to
line 146.
Any telephone in the system can be provided with the capability of
intercepting telephone calls made to another telephone. This "call
intercept" function is provided on Telephone A by connecting switch
147 to privacy line 20. With this connection, if Telephone C calls
Telephone B, periodic signal V'.sub.26 from Telephone C causes
Telephone B to ring and causes privacy switch 215 to deprive
privacy line 19 of signal T.sub.26. However, privacy switch 248
couples signals T.sub.26 to privacy line 20 which is connected via
switch 147 to privacy gate 122. Thus, if the handset of Telephone A
is picked up and Telephone B is dialed, signal V'.sub.26 will be
provided by privacy gate 122 to ring gate 121 and to call intercept
transmitter 151, a DC controlled switch, by line 125. Signal
V'.sub.26 is not transmitted by the call intercept transmitter 151
until the call intercept button on Telephone B (not shown) is
depressed thereby enabling the call intercept latch 152 which
controls said intercept transmitter 151.
The call intercept latch 152, a slip-flop circuit, is disabled when
the handset of Telephone A is removed from its cradle and voltage
PS, which is connected thereto from power switch 107 by line 108,
is applied; and is enabled by voltage CI, shown in FIG. 2f,
connected thereto from the power switch 107 over line 112 when the
call intercept button is depressed.
One output of the call intercept latch 152 is connected by line 153
to the link exchange network 126 and to bleep network 154. In
response to the CI voltage, the link exchange network, hereinafter
described, disconnects signal on line 102 from line 146 and
connects signal on line 125 to line 146. In addition, the bleep
network 154, a momentary switch, connects the bleep line 30, which
provides an audio tone, to the audio line 118. The audio tone is
heard at Telephone A and C and provides an indication that the call
from Telephone C has been intercepted.
The other output of the call intercept latch 152 is connected to
the call intercept transmitter by line 155 and provides thereto a
DC voltage (a logic 1) when the call intercept latch 152 is enabled
by voltage CI.
The DC voltage causes the call intercept transmitter to couple the
signal V'.sub.26 to the ring disable line 21 and to ring disable
receiver 137. Signal V'.sub.26 on the ring disable line 21 causes
the ring disable receiver 137 to disable the ring gate 121 on logic
card L.sub.A and the corresponding ring gate (not shown) on logic
card L.sub.C, thereby causing Telephone B to stop ringing.
The call intercept receiver 249 receives signal V'.sub.26 from the
ring disable line 21, signal T.sub.26 over line 202 from the fixed
time slot decoder 201, and disabling voltage PS over line 208 from
the power switch 207. So long as the handset of Telephone B is in
its cradle and signals V'.sub.26 and T.sub.26 are present, the call
intercept receiver 249 provides a pulse signal to call forward
privacy gate 250, which is an intergrator, and said gate provides
over line 256 a DC voltage (a logic 1) which disables privacy
switch 215 and privacy switch 248. The disabled privacy switches
deprive privacy lines 19 and 20 of signal T.sub.26 and therefore
indicates to the system that Telephone B is in use.
After the foregoing events related to the "call intercept" function
have occured, the party at Telephone C can talk with the party at
Telephone A even though he dialed Telephone B.
If it is desired to provide Telephone A with the capability of
interrupting a telephone conersation between two other telephones
in the system (Executive override), this can be achieved by
modifying its logic card, L.sub.A, as shown by the dotted line in
FIG. 5, so as to connect line 112 to privacy gate 122. Thus, when
the call intercept button is depressed, voltage CI enables the
privacy gate 122, regardless of whether privacy lines 19 or 20 are
providing pulses from the telephone called. In this mode of
operation, line 138 from the ring disable receiver is connected to
call forward privacy gate 150 and causes the gate to provide a DC
signal over line 158 to the link exchange network 126. This DC
signal prevents the line switching which would have taken place in
response to the application of voltage CI to the call intercept
latch 152. Thereafter, the party on Telephone A can talk to both
parties involved in the preexisting call.
Referring to FIG. 6, if the party having Telephone A wishes to have
calls made to him transferred, for example, to Telephone B, this
can be achieved by his picking up the handset, dialing Telephone
B's number and depressing the call forward button (A locking
switch-not shown) on Telephone A.
As previously described, when the handset of telephone A is removed
from its cradle, line 108 from power switch 107 connects voltage PS
to privacy switch 115 thereby disconnecting signal T.sub.46 from
privacy line 19. Line 109 from power switch 107 connects voltages
PS to ring disable gate 136 thereby allowing signal T.sub.46 to be
coupled to the ring disable line 21 to terminate the ringing of
Telephone A if it had been called.
However, depression of the call forward button after Telephone B
has been dialed causes a voltage CF, shown in FIG. 2g, to be
connected via line 113 to privacy switch 115 and ring disable gate
136 thereby connecting signal T.sub.46 to the privacy line 19 and
disconnecting signal T.sub.46 from the ring disable line 21 thus
making it appear to the other telephones in the system that the
handset of Telephone A is in its cradle. In addition, line 113
connects voltage CF to ring disable receiver 137 which in turn
provides a signal to the ring gate 121 so as to terminate ringing
at Telephone B.
If, for example, a party dials Telephone A from Telephone C, signal
V'.sub.46 is placed on to ring control line 18 and ring receiver
134. Ring receiver 134 is connected by line 159 to ring gate 121
and by line 135 to privacy switch 115. So long as signal V'.sub.46
is connected to the ring receiver 134, its outputs enable the ring
gate 121 thereby connecting V'.sub.26 pulses to the ring control
line 18 which cause Telephone B to ring and the privacy switch 115
is disabled thereby preventing signal T.sub.46 from being coupled
to privacy line 19 and causing Telephone A to look busy to the rest
of the system.
If the handset of Telephone B is picked up, signal T.sub.26 is
placed on the ring disable line 21 by Telephone,B, and the ring
disable receiver 137 which is also connected to the ring disable
line 21. The ring disable receiver 137 in response to signals
T.sub.26 and V'.sub.26, which is connected thereto by line 124,
provides a signal on line 138, which disables ring gate 121 and
causes Telephone C to stop ringing. In addition, the ring disable
receiver 137 causes call forward privacy gate 150 to send out a
signal on line 156, which also disables privacy switch 115, and a
signal on line 158, which enables the ring disable gate 136. When
the ring disable gate 136 is enabled, signal T.sub.46 is coupled to
ring disable line 21 and Telephone C stops providing signal
V'.sub.46 on ring control line 18. The absence of signal V'.sub.46
at the ring receiver 134 causes Telephone A to stop ringing and the
output on line 135 to drop to zero. This does not affect the state
of the privacy switch 115 but does cause the ring disable receiver
137 to provide a signal on line 138 which disables the ring gate
121.
Under the circumstances just described, Telephone A will appear to
be busy to the rest of the system. Audio signals from the Telephone
C will be modulated by V'.sub.46 on logic card L.sub.C and
transmitted to logic card L.sub.A. Logic card L.sub.A will
demodulate the incoming signal and use the recovered audio to
modulate signal V'.sub.26, and the resulting signal is transmitted
to logic card L.sub.B where the audio signal originating at logic
card L.sub.C is recovered and transmitted to Telephone C. Return
audio signals from Telephone B are similarly returned via Telephone
A to Telephone C.
If a party on Telephone C calls a party at Telephone A, audio
signals are modulated by analog switch 142 and reply audio signals
from Telephone C are selected by analog switch 143 for demodulation
by demodulator 144. It is to be noted, however, that when Telephone
A is answered, the power switch 107 is activated in the same manner
as if the handset at Telephone A had been picked up to make a call.
Accordingly, if the party at Telephone A dials the telephone number
of Telephone B, the party at Telephone B will be added to the
conversation via line 118, analog switches 140, 141 and demodulator
139. The party at Telephone B can also dial another party. Thus, a
conference call between many parties can be achieved if the called
party call someone else.
Referring to FIGS. 1 and 7, page music generator 11 provides audio
signals on page-music line 28 which is connected, for example, to
ring switch 114 on logic card L.sub.A. Normally, the ring switch
114 connects page-music line 28 to line 116 and thereby provides a
public address or music at Telephone A while its handset is in its
cradle. However, if Telephone A is called, the ring receiver 134
provides a DC signal (logic 1) on line 135 which causes the ring
switch 114 to disconnect the page music line 28 from line 116 and
to connect ring line 27 to line 116. If the handset of Telephone A
is removed from its cradle, line 108 connects voltage PS to the
ring switch 114,and causes the page music line 28 to be
disconnected from line 116,and connects line 116 to audio line 118.
Further, during the "call intercept" function, the DC signal (logic
1) on the call forward privacy gate 150 is connected by line 156 to
the ring switch 114 and causes the page music line 28 to be
disconnected from line 116 and connects line 116 to audio line 118.
Accordingly, a public address or music is only provided to the
telephones in the system when they are otherwise not in use.
Each logic card L.sub.A, L.sub.B, L.sub.C . . . L.sub.F in the
system includes a hold gate, which circuitwise is an inverter, a
push to talk receiver and a hold receiver which, respectively,
include a comparison circuit connected to a DC voltage producing
pulse stretcher, and a push-to-talk gate which circuitwise is an
AND gate.
Referring to FIG. 1 and 8, when, for example, Telephone A calls
Telephone B, the signal V'.sub.26 on line 125 is connected to the
hold gate 161 where it is inverted and connected to hold line 23.
Hold line 23 is connected to hold receiver 260 on logic card
L.sub.B. Line 202 connects signal T.sub.26 to the hold receiver 260
and when both signals T.sub.26 and inverted V'.sub.26 are present
at the hold receiver 260, it provides a DC signal on line 264.
In addition, signal V'.sub.26 on line 125 is connected to
push-to-talk gate 162, where it is inverted. When the call
intercept button is depressed, the voltage CI on line 112 is also
connected to the push-to-talk gate 162 and permits inverted signal
V'.sub.26 to be provided to push-to-talk line 24. Push-to-talk
receiver 263, which is similar to hold receiver 260, is conected to
push to talk line 24 and to line 202. Therefore, the push to talk
receiver 263 only provides a DC signal on line 265 when the call
intercept button is depressed.
The DC signal on line 264 and the DC signal on line 265 when the
call intercept button is depressed, may be used as control signals
for performing functions at a remote location. For example, the DC
signals may be used to provide a "hands free" call at Telephone
B.
A hands free operation at Telephone B is accomplished by connecting
line 264 and 265 to audio transceiver 266. Audio transceiver 266 is
connected to wires W.sub.B and is responsive to DC voltages on
lines 264 and 265. The DC voltage on line 264 causes privacy to be
maintained at Telephone B and the DC voltage on line 265 allows a
party at Telephone B to talk when zero volts are present (logic 0)
and allows a party at Telephone A to talk when a positive voltage
(logic 1) is present. This arrangement allows a party at Telephone
B to carry on a conversation without the need to hold the handset
of telephone B in his hands.
The logic cards in this system include subsystems which enable a
call to be made to one of a group of sequentially numbered
telephones.
In FIG. 9 there is shown subsystems on logic cards L.sub.G, L.sub.H
and L.sub.I which corresponding to Telephones G, H and I (not
shown) respectively, having telephone numbers 99, 98 and 97 and
comprising a group. In addition, FIG. 9 shows subsystems on logic
card L.sub.A which are used when Telephone A calls one of a group
telephone.
Assuming that Telephone H is in use, that logic cards L.sub.H and
L.sub.I provides signals T.sub.98 and T.sub.97 to stepping line 22,
and that Telephone A dials the number (97) of Telephone I, variable
time slot decoder 123 provides V.sub.97 to stepping line receiver
166. The stepping line receiver 166 is also connected to the
stepping line 22 and provides an output pulse on line 169 in
response to the simultaneous presence therein of signals T.sub.97
and V.sub.97. The output pulse on line 169 is connected to the dial
register and causes the dialed number to increase by 1 to 98.
Accordingly, the signal from the variable time slot decoder 123 to
the stepping line receiver 166 changes to V.sub.98. Signals
V.sub.98 and T.sub.98 at the stepping line receiver 166 cause
another pulse to be provided to the dial register 117 and its
stored number is again increased by 1 so that the variable time
slot decoder 123 provides signal V.sub.99 to the stepping line
receiver 166. Since the stepping line 22 does not provide a signal
T.sub.99, the dial register 117 does not experience a further
shift.
When the handset of Telephone A was removed from its cradle,
voltage PPS was connected by line 111 to a flip-flop circuit (not
shown) in stepping line inhibit gate 167. The PPS voltage set the
flip-flop and, via line 170 from the flip-flop, enabled the
stepping line receiver 166. Simultaneously, the dial register 117,
via line 171, provided a pulse to the stepping line inhibit gate
167 which is stretched therein for a period of time sufficient to
allow the "redialing" to take place. The trailing edge of the
stretched pulse resets the flip-flop and provides over line 170 a
signal which disables the stepping line receiver 166.
The group hunt privacy gates 672, 572, 472, respectively, are
connected to ring receivers 634, 534, 434 and to the voltage PS
outputs of the power switches 607, 507, 407 on logic cards L.sub.G,
L.sub.H, L.sub.I. So long as Telephones G and H are not off-hook or
ringing, their corresponding group hunt privacy gates 671, 572
provide a logic 0 to lines 67 and 68. Line 67 is connected to the
inputs 69 and 71, respectively, of stepping line transmitters 568
and 468, and line 68 is connected to the input 72 of stepping line
transmitter 468. So long as a logic 0 is on any input of a stepping
line transmitter, the transmitter will couple its corresponding
periodic signal T.sub.N to stepping line 22. Thus the arrangement
described causes incoming calls to the group of telephones to be
connected to the telephone having the highest number which is not
in use.
It was initially stated that stepping line transmitter 668 did not
provide a signal T.sub.99. This is due to the fact that all of its
inputs are connected to a logic 1, namely, a DC signal from a power
supply (not shown).
Referring to FIG. 10, Telephone A includes a signal lamp 81 and
series diode 82 across wires W.sub.A. Signal lamp 81 only lights
when Telephone A is rung. This is achieved by connecting a positive
voltage over line 106 to commutator 105 and by connecting a
negative voltage via line 173 from a power supply (not shown) to
the commutator 105 and by alternately connecting the positive and
negative voltage from the commutator to the input winding of the
transformer in transformer network 103. The negative voltage causes
current to flow in the series diode 82 and signal lamp 81 circuit
thereby giving off light.
Line 109 connects voltage PS to the commutator; line 135 connects
the ring receiver to the commutator 105 and supplies a positive
voltage when Telephone A is ringing, and line 26 connects positive
pulses from the pulse light generator 15 to the commutator 105.
When positive voltages are present on lines 109 and 135, the
negative voltage is connected by the commutator 105 to the wires
W.sub.A. If zero volts are on any of lines 26, 109, or 135, the
positive voltage is connected by the commutator to the wires
W.sub.A. Thus, if the handset of telephone A is removed from its
cradle, or Telephone A is not ringing, the signal lamp 67 goes
out.
Referring to FIG. 11, when the handset of Telephone A is removed
from its cradle, voltage PS is connected by line 108 to time out
circuit 175. This initiates a timing circuit which at the end of a
fixed amount of time (e.g., 30 sec.) causes the time out circuit
175 to provide a signal over line 176 to the power switch 107. This
signal causes the power switch to provide voltages PPS and PPS to
the dial register, thereby terminating the ringing at the called
telephone.
If the called telephone is picked up before the ringing is
terminated, the call forward privacy gate 150 provides over line
158 a 0 logic signal which disables the time out circuit 175 until
the handset of the called telephone is returned to its cradle. In
the "call forward" mode, voltage CF is connected by line 113 to the
time out circuit 175 and disables it so as not to disconnect
Telephone A from the Telephone to which calls are forwarded.
Thus, Telephone A, (except for the call forward mode) is
disconnected from a called telephone if the called party does not
answer his telephone within a prescribed amount of time, or after a
fixed amount of time after the called party hangs up.
The subsystems described heretofore are, as may be seen from the
functional description herein, simple analog or digital circuits.
For example, the link exchange network 126, the privacy switch 115,
the privacy gate 122 and the ring disable receiver 137 will be more
fully described herein below.
The link exchange network 126 either provides a signal V'.sub.N on
line 146 or signals V'.sub.N and T.sub.46, respectively, on lines
145 and 146, depending upon whether a logic 1 signal corresponding
to the "call intercept" mode of operation, or a logic 0 signal,
corresponding to the "executive override" mode of operation, is
present on line 153.
Referring to FIGS. 5 and 12, when the CI button is depressed, a
change from logic 1 to logic 0 on line 153 causes the
differentiating network comprising capacitor 1001 and gate 1002 to
provide a pulse to gate 1003. In the "call intercept" mode, a logic
1 signal is also applied to gate 1003 via line 158 and therefore,
the pulse provided by gate 1003 is inverted and applied to an R-S
flip-flop comprising gates 1004 and 1005. The inverted pulse resets
the flip-flop and causes a logic signal to be applied to gate 1008
via line 1006 thereby coupling the V.sub.N signal on line 125 to
line 146.
The voltage PS on line 108 sets the flip-flop when the handset of
Telephone A is removed from its cradle. In the "executive override"
mode, a logic 0 is applied to gate 1003 and the flip-flop remains
set, thereby providing a logic 1 signal to gates 1009 and 1010 via
line 1007. A logic 1 signal at gates 1009 and 1010 allows the
gates, respectively, to couple signal T.sub.46 one line 102 and
signal V'.sub.N on line 125 to lines 146 and 145.
The function of the privacy switch 115 is to control the passage of
an inverted signal T.sub.46 out to privacy line 19 in order to
incicate by its presence that Telephone A is not busy and by its
absence that Telephone A is busy.
Referring to FIGS. 4, 5, 6, and 13, the fixed time slot decoder
provides an inverted T.sub.46 signal over line 102 to gate 1014.
When Telephone A is not busy, this signal is coupled to privacy
line 19 by gates 1014 and 1015. The presence of a logic 1 signal on
either of lines 135 and 156, or both of lines 108 and 113, will
cause a logic 0 to be applied to gate 1015 via line 1016 thereby
inhibiting gate 1015 and depriving the privacy line 19 of a pulse
signal.
If it is decided that privacy during ringing is not desired, as
with privacy switch 248, shown in FIG. 5, this may be achieved by
removing gate 1013 from the circuit shown in FIG. 13.
The function of the privacy gate is to sense the presence of pulse
on privacy lines 19 and 20 and to provide a signal V'.sub.N when
pulses are present in its corresponding time slot.
Referring to FIG. 4, 5, 6, and 14 the output signal V.sub.N on line
124 from the variable time slot decoder 123 is connected to gate
1021 and transmitted via gate 1022 to line 125 only if inhibit line
127 provides a logic 1 to gate 1021. The line 127 is an output of a
flip flop circuit, comprising gates 1019 and 1020, which is reset
by voltage PPS on line 111 when the handset of Telephone A is
picked up. When the flip-flop is reset, a logic 0 is applied to
gate 1021 thereby preventing signal V.sub.N from being coupled to
gate 1022.
When a D.C. voltage signal or voltage CI via line 112 is connected
to line 1024, or a pulse signal T.sub.N from either privacy line 19
or 20 is connected to gate 1017, a pulse is provided on line 1025
to gate 1018. If the pulse signal on line 124 coincides with the
pulse signal on line 1025, an output pulse is provided to gate 1019
which sets the flip-flop, thereby applying a logic 1 to gate 1021
and allowing V'.sub.N signals on to line 125.
Generally, the purpose of the ring disable receiver 137 is to
receive signals from the ring disable lines 21 which are present
during a particular time interval assigned to a called telephone.
The presence of such signal is an indication that the called party
has picked up his telephone and that ring tone should be
terminated. Therefore, the output 138 of the ring disable receiver
137 is applied to the ring gate 121 of Telephone A to inhibit its
operation.
Referring to FIG. 4, 5, 6, and 15, this is achieved by connecting
the signals on ring disable line 21 to gate 1026 where they are
inverted and applied to gate 1027. If the signal V.sub.N from the
variable time slot decoder 123 on line 124 and the inverted signal
have pulses which occur at the same time, gate 1027 will provide an
output signal on line 138. Further, a negative step voltage
provided by either line 113 or line 135 causes a positive pulse to
be applied to gate 1027 which lasts for more than a clock cycle
thereby allowing a pulse to be transmitted to line 138 when the
call forward button is depressed or when the ring receiver output
on line 135 drops to a logic 0.
It is to be understood that the description herein of a preferred
embodiment according to the invention is set forth as an example
thereof and is not to be construed or interpreted as a limitation
on the claims which follow and define the invention.
* * * * *